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Scarce primes (Posted on 2011-01-10) Difficulty: 2 of 5
A repunit is a number consisting solely of ones (such as 11 or 11111).
Let us call p(n) a 10-base integer represented by a string of n ones, e.g. p(1)=1, p(5)=11111 etc.
Most of the repunit numbers are composite.
2, 19,23,317 are the first four indices of prime repunits.

Prove: For a prime repunit p(n) to be prime, n has to be prime.

No Solution Yet Submitted by Ady TZIDON    
Rating: 3.6667 (3 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Hints/Tips re: Another proof - not a proof | Comment 6 of 10 |
(In reply to Another proof by Gamer)

The "proof " errs:

yoo wrongly defined  q

In your example just exchange x and y ,you get 111*101,clearly

not p(6)

Edited on January 11, 2011, 2:53 am
  Posted by Ady TZIDON on 2011-01-11 02:10:16

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